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A novel methodology for characterizing the morphology distribution of filler agglomerates in elastomer composites is presented based on laboratory-sourced X-ray tomography. Various feature extraction methods (via, e.g., image-processing filters, segmentation) and selection tools (Spearman's rank correlation coefficient) combined with K-means unsupervised clustering algorithm were developed for identifying the distinct morphological classes in model materials (carbon-filled ethylene propylene diene monomer rubber). The interest of this methodology was demonstrated by precisely differentiating the materials compounded with different processing parameters. For instance, in this example, thanks to this analysis, it was found that introducing the filler before the elastomer in internal mixer tends to favor more structured agglomerates.

International audience; Lithium (Li) metal is the most promising negative electrode to be implemented in batteries for stationary and electric vehicle applications. For years, its use and subsequent industrialization were hampered because of the inhomogeneous Li + ion reduction upon recharge onto Li metal leading to dendrite growth. The use of solid polymer electrolyte is a solution to mitigate dendrite growth. Li reduction leads typically to dense Li deposits, but the Li stripping and plating process remain nonuniform with local current heterogeneities. A precise characterization of the behavior of these heterogeneities during cycling is then essential to move toward an optimized negative electrode. In this work, we have developed a characterization method based on X-ray tomography applied to model Li symmetric cells to quantify and spatially probe the Li stripping/plating processes. Ante-and postmortem cells are recut in smaller cells to allow a 1 μm voxel size resolution in a conventional laboratory scanner. The reconstructed cell volume is postprocessed to numerically reflatten the Li electrodes, allowing us a subsequent precise measurement of the electrode and electrolyte thicknesses and revealing local interface modifications. This in-depth analysis brings information about the location of heterogeneities and their impact on the electrode microstructure at both the electrode grains and grain boundaries. We show that the plating process (reduction) induces more pronounced heterogeneities compared to the stripping (oxidation) one. The existence of crosstalking between the electrodes is also highlighted. In addition, this simple methodology permits to finely retrieve and then surface map the local current density at both electrodes based on the local thickness change during the redox process.

International audience; The term agroforestry covers practices that are promoted to maintain or even enhance biodiversity. However, the relationship between agroforestry and invasive species is rarely addressed, even though the spread of such species is an important issue, not only ecologically but also economically and socially. Over the past few decades, humans have greatly accelerated the process of biological invasions, to such an extent that they are now recognized as the second cause of rapid decline in biodiversity. In France (as in other parts in Europe), abandonment of agricultural land in remote areas is a major problem having socio-economic, landscape and environmental implications. The objective of the research presented here was to find a method for studying the relationship between traditional agroforestry systems and invasive species, despite a lack of available data. We investigated the evolution of a traditional agroforestry system in the Pyrenean foothills, where invasive species are abundant, by implementing two complementary methods: (1) interviews highlighting the local stakeholders' perception of landscape evolution, invasive species and the challenges they represent for the local traditional agroforestry landscapes, and (2) detailed mapping of an area occupied by invasive plants, by means of very high-resolution spatial technologies using UAV's and aerial photography. The results show that invasive species have spread in relation with the abandonment of agricultural land, which has also led to "landscape closure" by the encroachment of natural afforestation. They also underline the difficulty of assessing the spread of invasive species. This situation is of major importance in terms of land-use planning, as the various stakeholders have different perceptions of the problem, and it raises questions about the sustainability of practices and territories.

Self-healing strategies aim at avoiding part repair or even replacement, which is time consuming, expen-sive and generates waste. However, strategies for metallic systems are still under-developed and solid-state solutions for room temperature service are limited to nano-scale damage repair. Here we propose a new healing strategy of micron-sized damage requiring only short and low temperature heating. This new strategy is based on damage localization particles, which can be healed by fast diffusing atoms of the matrix activated during heat treatment. The healing concept was successfully validated with a com-mercial aluminum alloy and manufactured by Friction Stir Processing (FSP). Damage was demonstrated to initiate on particles that were added to the matrix during material processing. In situ 2D and 3D nano -imaging confirmed healing of the damaged material and showed that heating this material for 10 min at 400 degrees C is sufficient to heal incipient damage with complete filling of 70% of all damage (and up to 90% when their initial size is below 0.2 mu m). Furthermore, strength is retained and the work of fracture of the alloy is improved by about 40% after healing. The proposed Programmed Damage and Repair healing strategy could be extended to other metal based systems presenting precipitation. (C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Longitudinal tensile failure of unidirectional fibre-reinforced composites remains difficult to predict accurately. The key underlying mechanism is the tensile failure of individual fibres. This paper objectively measured the relevant input data and performed a detailed experimental validation of blind predictions of six state-of-the-art models using high-resolution in-situ synchrotron radiation computed tomography (SRCT) measurements on two carbon fibre/epoxy composites. Models without major conservative assumptions regarding stress redistributions around fibre breaks significantly overpredicted failure strains and strengths, but predictions of models with at least one such assumption were in better agreement for those properties. Moreover, all models failed to predict fibre break (and cluster) development accurately, suggesting that it is vital to improve experimental methods to characterise accurately the in-situ strength distribution of fibres within the composites. As a result of detailed measurements of all required input parameters and advanced SRCT experiments, this paper establishes a benchmark for future research on longitudinal tensile failure The research leading to these results has been conducted in the framework of the FiBreMoD project and has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 722626. Compressive tests on the neat epoxy resin were performed at the mechanical lab of the Institute of Mechanics, Materials and Civil Engineering (IMMC), Université Catholique de Louvain (UCLouvain) with the kind support of J. Chevalier and T. Pardoen. M.J. Emerson from QIM, Technical University of Denmark (DTU) is thankfully acknowledged for the handson training sessions and support of the Insegt Fibre segmentation toolbox. Support of C. Schlepütz from TOMCAT beamline at Swiss Light Source for optimising the acquisition settings during the beamtimes under proposal IDs 20161157 and 20171494 is thankfully acknowledged. J.M. Guerrero would like to acknowledge the grant BES-2016-078270 from the ‘Subprograma Estatal de Formación del MICINN’ cofinanced by the European Social Fund, and all authors from the University of Girona acknowledge the funding from the Spanish project RTI2018-097880-B-I00. The work of M. Hajikazemi forms part of the research programme of DPI, project 812T17. S. Pimenta acknowledges the funding from the Royal Academy of Engineering in the scope of her Research Fellowship on “Multiscale discontinuous composites for high-volume and sustainable applications” (2015-2019). R.P. Tavares and P.P. Camanho would like to thank the financial support provided by FCT - Fundação para a Ciência e a Tecnologia through National Funds in the scope of project MITP-TB/PFM/0005/2013

International audience; Most of the post-Lithium-ion (Li-ion) devices, such as Li–sulfur, Li–O2, or all-solid-state Li batteries, have in common an negative electrode made of metallic Li.1 The main failure mode of Li based batteries is the inhomogeneity of the Li electrodeposits onto the Li metal negative electrode during charge steps, leading to dendrite growth and low Coulombic efficiency.2 Tomography and radiography imaging techniques are now vastly employed for battery materials analysis thanks to the possibility to perform noninvasive in situ and operando experiments.3 X-ray tomography is a powerful tool for studying dendrites as it provides useful information about their locations, dynamics, and microstructures. However, the use of neutron tomography is scarcely reported for Li electrodeposit analysis due to the difficulty to reach sufficient image resolution to capture the deposit microstructure, that is, typically below 10 to 20 µm. Furthermore, the different interactions of X-rays and neutrons with Li, which has significantly different opacity in the two cases, make the two techniques highly complementary.4 Notably, the capacity of neutrons to discern different Li isotopes is pivotal to get insight into the composition of Li deposits, by distinguishing between Li originating from an electrode (6Li in this study) and Li originating from the Li salt electrolyte (mainly in 7Li here). Indeed, the theoretical linear neutron attenuation coefficient of 6Li is about 15 and 2,000 times larger than that of natural Li and 7Li, respectively.In this study, we report as a proof of concept, an in situ neutron tomography imaging of Li electrodeposits in a cycled Li symmetric cell (see Figure 1).5 The electrochemical cell comprises a natural Li electrode, a 6Li electrode, and a deuterated liquid electrolyte. The neutron tomography is compared with X-ray tomography images of the same electrochemical cell acquired both at an X-ray synchrotron beamline and at a laboratory X-ray tomograph. Neutron tomography is shown to be compatible with in situ analysis and capable of capturing the overall morphology of the Li deposits in good accordance with X-ray tomography analyses.

Engineering fracture mechanics 274, 108771 (2022). doi:10.1016/j.engfracmech.2022.108771, This paper presents the impact of Carbon Blacks agglomerates, at different concentrations, on crack propagation mechanisms in a Carbon black (CB) filled Ethylene Propylene Diene Monomer (EPDM) elastomer. As shown by Transmission electron microscopy, these CB agglomerates (CB$_{aggl}$) consist of aggregates clusters with interpenetrating elastomer, and for this reason, are soft and deformable. Crack tip observation using X-ray tomography demonstrates that these CB$_{aggl}$ can either undergo fracture or arrest/ deviate a crack during its propagation. This causes higher energy dissipation at the crack tip, which contributes to the dissipative component of the strain energy release rate G. For this reason, it is found that among the two materials tested with a significant amount of CB$_{aggl}$ (more than 3%), the material with the highest concentration has a slower crack propagation speed at high G., Published by Elsevier Science, Kidlington

In this work, we study the effect of crystallographic orientation and applied triaxiality on the growth of intragranular voids. Two 3D full-field micromechanics methods are used, the dilatational visco-plastic fast-Fourier transform (DVP-FFT) and the crystal plasticity Finite Elements (CP-FE), both of which incorporate a combination of crystalline plasticity and dilatational plasticity. We demonstrate with several select cases that predictions of void growth from both formulations agree qualitatively. With the more computationally efficient DVP-FFT, additional effects of polycrystalline microstructure and the influence of nearest neighborhood are investigated. Crystals bearing a single intracrystalline void are studied in three types of 3D microstructural environments: isolated single crystals, individual equal-sized grains within a regular polycrystal, and individual variable sized grains within a polycrystal with grains and voids randomly located. We show that loading type plays a significant role. In strain-rate controlled conditions, voids in the hardest [111]-crystals grow the fastest in time, whereas in stress-controlled conditions, voids in the softest [100]-crystal grow the fastest in time. The analysis reveals that on average void growth is slower for the same starting orientation in the polycrystal than in the single crystal. We find that at the highest triaxiality tested that the correlation between crystal orientation and void growth rate in the polycrystal strengthens, drawing closer to that seen in the isolated single crystals. These results and model can help guide the microstructural design of polycrystalline materials with high strength and damage-tolerance in high-rate deformation.

Additive manufacturing of large scale parts is an innovative, challenging research field, with the potential of producing parts with complex structures, specific functional and structural properties. In this study, binder jetting was employed using two different large scale printers to fabricate non-structural parts made of artificial stone. The printing bed was comprised of aggregates (River sand and Poraver expanded glass) and reactive magnesium oxide and potassium phosphate powders, which were activated by selectively depositing water, layer after layer. The exothermic reaction between reactive powders and water generates in situ a hydraulic inorganic binder, that binds the aggregates in the bed. The reaction parameters were controlled to achieve a fast setting, enabling rapid printing at the macro-scale (in the range of tens of centimeters or meters). The influence of the voxel size of the printers on the microstructure and printing quality of the fabricated parts, their physical and mechanical properties as well as the in situ formation of the cement phase were investigated by X-ray microtomography.

Objective Resin-based composites are widely used in dental restorations; however, their volumetric shrinkage during polymerization leads to several issues that reduce the restoration survival rates. For overcoming this problem, a deep study of shrinkage phenomena is necessary. Methods In this study, micro-tomography (μ-CT) is combined with digital volume correlation (DVC) to investigate the effect of several factors on the polymerization strain of dental composites in model cavities: the presence/absence of an adhesive, the use of transparent/blackened cavities, and irradiation times between 1 and 40 s. Results The results indicate that the presence of an adhesive at the interface between the cavity and composite does not reduce the total strain but instead limits it to a preferential direction. In addition, regardless of the conditions, the main strain is generated along the axis parallel to the polymerization irradiation (the vertical axis). Finally, the total strain appears to occur in the first 5 s of irradiation, with no further evolution observed for longer irradiation times. Significance This work provides new insight into resin-based composite shrinkage and demonstrates the benefit of coupling DVC and μ-CT to better understand the degradation mechanisms of these materials.

International audience; The electronic conductivity, at the multiscale, of lithium-ion positive composite electrodes based on LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2 and/or carbon-coated LiFePO_4, carbon black and poly(vinylidene fluoride) mixture is modeled. The electrode microstructures are acquired numerically in 3D by X-ray tomography and FIB/SEM nanotomography and numerically segmented to perform electrostatic simulations using Fast Fourier Transform (FFT) method. Such simulations are easy and quick to perform because they are directly computed on the grid represented by the voxels in the 3D volumes. Numerical results are compared with experimental measurements of the multiscale electronic conductivity by broadband dielectric spectroscopy (BDS). A good prediction is realized for the bulk conductivities of the C/LiFePO_4 phase and the CB/PVdF mixture. The combination of X-ray and FIB/SEM tomography, FFT simulation method, and BDS is thus well adapted to understand the influence of the electrode composition and microstructure on its electronic conductivity.

Conférence en distanciel; International audience; The rapid spread of invasive plant species (IPS) over several decades has led to numerous impacts on biodiversity, landscape and human activities. Early detection and knowledge on their spatiotemporal distribution is crucial to better understand invasion patterns and conduct appropriate activities for landscape management. Therefore, remote sensing provides great potential for detecting and mapping the spatial spread of IPS. The study presents a mapping of IPS (Reynoutria japonica and Impatiens glandulifera) over the last decade, on two sites located in the central Pyrenees in the southwest of France, from very high resolution RGB aerial photographs. A supervised classification based on the random forest algorithm was performed using pixel attributes. The original spectral bands (RGB) were used, to which vegetation indices and textures were added to improve the detection. The classification models yielded a mean prediction accuracy (F-score) of 0.90 (0.87 to 0.92) at the site 1 and 0.87 (0.81 to 0.91) at the site 2. Results show that the expansion of IPS is closely related to the presence of corridors (e.g., roads, power lines) and to environments disturbed by human activity such as land clearing.

International audience; Single-chamber microbial fuel cells (MFCs) with air-cathodes and new anodes made of stainless steel entangled wires are developed. Increasing the cathode surface area significantly increases performances (doubling the cathode surface area increases the maximum power by +23,3 % and tripling it by +59,8 %). By contrast, increasing the anode surface area rapidly leads to performance saturation (doubling the anode surface area increases the maximum power by +37.8 % but tripling it by only +39.3 %). In addition, decreasing the electrode spacing from 6 cm to 4 cm improves the maximum power by +21.3 % and from 4 cm to 2 cm by +27.9 %. This results permit to optimally dimension the architecture of the MFC in order to maximize energy production while minimizing the amount of materials used to minimize costs. This in turn is likely to enable the development of effective solutions for energy harvesting.

International audience; Laser Powder Bed Fusion (LPBF) printing is used for manufacturing conformal cooling injection molds with internal cooling channels. Currently, the steel used to manufacture such molds by LPBF is the maraging 18Ni300. However, this steel is softer at high temperatures and less resistant to corrosion than the reference steel, the AISI H11. Moreover, 18Ni300 contains cobalt, an element that can be harmful to the health of people handling powders made of this steel. In order to find a cobalt-free alternative to 18Ni300, the printability of three different types of steel is studied: maraging stainless steels (CX, L40), martensitic non-stainless steels (42CD4, H11, H13, PM2012) and martensitic stainless steels (X15TN, PM420). The printability of those eight steels is studied through their mechanical properties (Rockwell hardness, Charpy impact test), their internal defects and surface roughness (X-ray tomography), the presence of cracks (optical microscope), and also through their microstructure (X-ray diffraction) in the as-built state. The results show that the stainless steels (PM420, X15TN, L40 and CX) exhibit interesting as-built properties allowing them to be considered as a possible alternative to the maraging steel 18Ni300 to produce LPBFed injection molds. A conformal cooling injection mold was then printed as a demonstrator.

A model able to reproduce the tensile response of single continuous-filament yarns based on parameters derived from geometrical descriptors is presented in this paper. Samples of yarns made of poly...

This paper is dedicated to the in situ follow up of the setting of an α plaster using synchrotron X-ray tomography, with a high spatial resolution, down to 0.3 µm (0.16 µm voxel size), and a high time resolution with a scan every 30 s. This combination of spatial and time resolution is amongst the best reported in the literature so far and is of particular interest for the study of moderately rapid transformation of the microstructure at a small scale. It enables to characterize both the dissolution of hemihydrate particles and the precipitation of gypsum crystals. A dissolution rate for the hemihydrate particles is determined, in good coherence with previous work on β plaster using lab X-ray tomograph. A thickening of gypsum crystals with hydration time is also noted. A quantitative analysis of hydration is performed through the calculation of a microstructural degree of reaction from the X-ray tomography volumes, after peak deconvolution of the gray value histogram at different hydration times.

We performed in-situ tensile tests on two carbon fibre/epoxy composites with continuous scanning using synchrotron computed tomography (CT). Both composites were cross-ply laminates, and two specimens were tested for each compos- ite. The voxel size was sufficiently small to recognize individ- ual fibres and fibre breaks. For each test, 16-19 volumes were reconstructed, cropped down to the 0° plies and analysed to track fibre break and cluster development. This dataset provides the last CT volume before failure for each of the four specimens as well as the individual fibre break locations in all reconstructed volumes. These data are then plotted against predictions from six state-of-the-art strength models. The target is that these data become a benchmark for the development of new models, inspiring researchers to set up refined experiments and develop improved models. © 2021 Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

International audience; The discharge rate performance of NMC532-based electrodes designed for EV application were measured between 0 °C and 40 °C and were compared to the predictions of the electrolyte limited penetration depth model [Gallagher et al., J. Electrochem. Soc. 163, A138 (2016)], also called diffusion limited current density model [Heubner et al., J. Power Sources 419, 119 (2019)]. To support this analysis, we took into account the actual microstructure of the electrodes, previously characterized by FIB/SEM tomography, and their measured and/or simulated transport properties. We show that the performance of NMC532 electrodes, even with a low carbon content below the percolation threshold, are not limited by electrons transport through the electrode due to the high intrinsic conductivity of this active material. At 40 °C, the swelling of the PVdF by the electrolyte solvents penalizes performance, especially as the binder content is high. Above all, the current density at which a brutal decrease in capacity occurs is well predicted by the model, although by reducing the porosity to its percolated micrometer sized fraction. This is in good agreement with the numerical simulations of the ionic transport properties.

National audience; Les hydrosystèmes karstiques sont des milieux sensibles aux variations climatiques et aux pressions anthropiques ; ils sont doc d’excellents modèles pour étudier leurs impacts sur les ressources en eau et sur les cycles biogéochimiques du carbone et de l’azote, aujourd’hui fortement perturbés par les changements d’occupation des terres. Ainsi, la recolonisation par la forêt de terres abandonnées suite à la déprise agricole favorise la production de matières organiques dans les sols. Ces changements induisent une augmentation de la pression partielle en CO2 (pCO2) dans les sols et dans les réseaux karstiques qui favorisent la dissolution des carbonates, mais aussi la production de carbone organique dissous (COD) dans les eaux. Ainsi, une augmentation de la pCO2 dans les cavités karstiques (Ek & Godissart, 2014) et une évolution significative de la composition chimique des eaux de drainage ont pu être observées sur les bassins versants karstiques français (Binet et al., 2020 ; Ulloa-Cedamanos et al., 2020), grâce aux données collectées depuis parfois près de 50 ans dans le cadre du SNO Karst (IR OZCAR). Parallèlement à ces évolutions, on observe des tendances à long terme dans les fluctuations hydroclimatiques (notamment une augmentation de la température de l’air) et dans l’évolution des paysages avec un abandon progressif des terres cultivées au profit des friches (Houet et al., 2012). Dans le cadre de la ZA PYGAR, le bassin versant karstique du Baget (13 km2), observatoire du SNO Karst (près de Moulis, Pyrénées ariégeoises, entre 500 et 1500 m), a été retenu comme site pilote pour développer une méthode de reconstitution dans le temps de l’évolution des paysagesqui sera mise au regard de l’évolution des débits et de la qualité des eaux, suivis depuis près de 50 ans. Pour mettre au point la méthode, nous avons reconstitué l’évolution de l’occupation des sols depuis 1948, à intervalles de 8 ans (à l’exception de la période 1947-1963), à partir des images satellites depuis les années 2000 (SPOT 2 et 4, Sentinel 2) et des photographies aériennes pour les périodes plus anciennes. Cette méthode a consisté à (i) utiliser les données de l’inventaire forestier et de photo-interprétation (google earth ) pour développer une procédure de classification de l’occupation du sol à partir d’images satellites (SPOT, Sentinel) et primitives associées (texture), (ii) appliquer cette méthode de classification de l’occupation du sol au traitement des photos aériennes anciennes géo-référencées, (iii) développer un indicateur multicritère d’ouverture/fermeture du milieu, et (iv) évaluer l’intensité du changement d’occupation du sol en termes de surfaces relatives et d’ouverture des milieux, de fragmentation et de localisation. Pour la reconstitution dans les temps anciens, les formations végétales ont été in fine regroupées en 3 grands groupes, en fonction de leur couverture au sol, de la densité de biomasse et de leur rôle dans l’ouverture des milieux. Les résultats présenteront la démarche et la méthodologie misesen oeuvre, ainsi que l’évolution spatio-temporelle des surfaces occupées par chaque formation, quantifiées à partir de l’indicateur multicritère développé.

International audience; Experimental conductivity measurements, obtained on NMC 532 -based electrodes with markedly different porosities and made with percolating and non-percolating CB/PVdF phase, are compared with full-field numerical predictions. These ones are based on segmented nanotomography images and phase bulk properties and contain no tunable parameter. A good agreement between the calculated and measured transport properties is observed. 3D current density fields give insights on the microstructure impacts on the current density distribution. Ionic transport is dominated by low tortuosity micrometric channels. Results also highlight the presence of “dead areas” in porosity that are crossed by a very low ionic current showing that, at high rate, the effective porosity may reduce to the micrometric pore network. For electronic conductivity, the CB/PVdF mixture percolation threshold is evaluated at 6%–7% in volume. Even below this key value threshold, CB/PVdF aggregates significantly improve electronic conductivity by forming gateways between NMC clusters thus minimising the constriction resistances between them. The size of the representative volume element relative to electronic and ionic conductivities is also investigated.

The tensile behavior of individual struts extracted from an open-cell aluminum foam is investigated here. X-ray microtomography is used to characterize the initial state of the struts in 3D, before micro-tensile testing performed under digital image correlation. A microstructure-sensitive finite element (FE) model is run afterwards, using a FE mesh conforming to the tomography volume and a constitutive model based on Gurson-Tvergaard-Needleman (GTN) porous plasticity. The model is made dependent on the local measure of intermetallic particles volume fraction in order to account for their embrittlement effect. Model and experiments delineate the first order effect of structure and shape on the plastic flow and fracture of the struts. The distribution of intermetallic particles influences fracture location only where minor variations of cross-section can be found. The model performs well at predicting the fracture zones but misses additional ingredients to assess the dispersion of yield strength among the struts.

Better understanding of how the microstructure of composite electrodes affect their electrochemical performance is still required to achieve Lithium ion batteries of higher energy and power densities [1]. Novel opportunity for progressing in this direction and explore relationships between composite electrode microstructure and electrochemical performance is implementation of X-ray computed tomography (XRCT) and focused ion beam in combination with scanning electron microscopy (FIB-SEM) techniques [2]. Sophisticated characterization techniques such as broadband dielectric spectroscopy (BDS) [3] and/or Pulsed Field Gradient Spin - Echo NMR (PFG-SE NMR) [4] can also be used to measure transport properties and relate them to the composite electrode microstructure. Finally, numerical simulations performed on 3D volumes acquired by XRCT or FIB/SEM is a powerful tool to calculate effective transport properties and finely analyze the impact of the composite electrode microstructure [5]. In this work, the microstructure of LiNi0.5Mn0.3Co0.2O2 (hereafter called NMC532)-based positive composite electrodes designed for EV applications were deeply investigated in relationship with their electrical properties. The composite electrode microstructures were acquired numerically in 3D at different scales by X-ray tomography and FIB-SEM tomography. Image analysis tools were developed to extract specific textural parameters (e.g. distribution and percolation of the carbon/binder mixture, type and tortuosity of the porosity, contact area of the active material with these other phases) to assess the electronic and ionic conductivities at different locations and spatial scales. In complement, 3D-resolved simulations with the Fast Fourier Transform (FFT) method were carried out to calculate the effective electronic and ionic conductivities of the composite electrodes and characterize the local current density paths for both type of charges (electrons and ions). From our results, it becomes apparent that it is possible to find a good compromise between the electronic and ionic conductivities that results in improved electrochemical performance by optimizing the microstructure. Acknowledgments Financial funding from the ANR program no. ANR-15-CE05-0001-01 is acknowledged. We also acknowledge the CLYM (Consortium Lyon Saint-Etienne de Microscopie) for the access to the FIB/SEM device used in this study. References [1] D. Mohanty, E. Hockaday, J. Li, D.K. Hensley, C. Daniel, D.L. Wood III, Effect of electrode manufacturing defects on electrochemical performance of lithium-ion batteries: Cognizance of the battery failure sources, J. Power Sources 2016, 312, 70-79. [2] N. Besnard, A. Etiemble, T. Douillard, O. Dubrunfaut, P. Tran-Van, L. Gautier, S. Franger, J.-C. Badot, E. Maire, B. Lestriez, Multiscale morphological and electrical characterization of charge transport limitations to the power performance of positive electrode blends for lithium-ion batteries, Adv. Energy Mater, 2017, 7, 1602239. [3] J.-C. Badot, B. Lestriez, O. Dubrunfaut, Interest in broadband dielectric spectroscopy to study the electronic transport in materials for lithium batteries, Mater. Sci. Eng. B - Adv. Funct. Solid-State Mater., 2016, 213, 190-198. [4] S. J. Tambio, M. Deschamps, V. Sarou-Kanian, A. Etiemble, T. Douillard, E. Maire, B. Lestriez, Self-Diffusion of Electrolyte Species in Model Battery Electrodes Using Magic Angle Spinning and Pulsed Field Gradient Nuclear Magnetic Resonance, J. Power Sources, 2017, 362, 315-322. [5] F. Cadiou, F. Willot, B. Lestriez, T. Douillard, A. Etiemble, J-C. Badot, O. Valentin, E. Maire, Numerical simulation of effective electrical conductivity of Lithium-ion battery positive electrodes, J. Electrochem. Soc., 2019, 166, A1692-A1703. Figure 1

Polyelectrolytes are promising binders for sulfur cathodes of Li/S batteries, with an ability to control the diffusion of polysulfides into the electrolyte, but their impact on the microstructural ...

The influence of microstructure and stress state, as defined by the stress triaxiality and Lode parameter, on micro-void nucleation was evaluated experimentally for two 800 MPa Advanced High Strength Steels (AHSS), one a Complex-Phase CP800 alloy, with a ferritic-bainitic microstructure, and the other a Dual-Phase DP780 ferritic-martensitic steel. Four plane stress specimen geometries (simple shear, hole tension, v-bend and biaxial Nakazima) were adopted, providing stress triaxiality and Lode parameter values ranging from in-plane shear to biaxial tension under approximately constant stress states until failure. This approach facilitated determination of the relationship between void nucleation and macroscopic stress state. Damage histories were developed from interrupted samples using 3D micro-tomography and quantitative stereology measurement of void nucleation paired with in situ digital image correlation (DIC) strain measurements during the mechanical testing. The trends in damage evolution are strongly linked to the stress state, with very little void nucleation under shear deformation but extensive void damage under biaxial tension for both materials. A dependency of the nucleation rate on Lode parameter was also demonstrated. A higher rate of damage accumulation was observed for the DP780 steel compared to damage in the CP800 steel for all loading conditions highlighting the strong influence of initial microstructure. An analytical framework is proposed to obtain the local stress-state and equivalent plastic strain history from direction integration of the measured DIC strain histories, using a measured hardening law and assumed anisotropic yield function (Yld91) to develop the link between nucleation and the macroscopic stress state. A stress-state dependent nucleation model is proposed by introducing a nucleation strain surface as a function of stress-triaxiality and Lode parameter using a modified form of the strain-based Chu and Needleman nucleation criterion.

Cold sintering is a promising route towards the manufacturing of dense ceramics at mild processing conditions, but our poor understanding of the process has prevented the wider spread of this attractive densification approach. Using nanovaterite powders with well-defined multiscale morphology, we perform in-situ X-Ray tomography on compacts subjected to controlled mechanical load and quantify the multiscale deformation processes responsible for the water-assisted cold sintering of this powder with the help of instrumented indentation experiments at the micro- and nano-scale. Our results reveal the crucial effect of water in promoting the macroscopic densification process and highlight the dominant role of the nanoparticle network inside agglomerates in controlling the cold sintering of compacts at high mechanical loads. By providing new insights into the deformation processes responsible for the densification effect, this study can potentially guide the discovery of novel chemical compositions and particle morphologies that can be more easily densified through room-temperature cold sintering with water.

Thin Ti-6-Al-4V tensile fatigue specimens were specifically designed to mimic struts of a lattice structure. Those samples were subjected to HIP and chemical etching that are thought suitable for complex geometries (machining was excluded). The effect of each post-treatment, as well as their combination on the fatigue performance is evaluated and quantified. Fatigue cracks are found to systematically initiate from surface defects. An original approach based on a full-3D non-destructive characterization by X-ray microtomography is developed to identify the population of those defects and rank them based on their size. Kitagawa-Takahashi diagrams are then used as a predictive tool regarding fatigue failure of samples containing defects. We show that ranking the defect size alone does not fully reflect the harmfulness of the identified defects.

Sheared edge failure is one of the major problems associated with the forming of advanced high strength steels (AHSS) such as dual-phase (DP) steels. To improve the performance of AHSS in industrial forming operations, ferritic-bainitic complex-phase (CP) steels have been developed and are gaining attention in academia as well as industry. The present work aims to investigate the influence of microstructure on micro-void (damage) evolution during the edge stretching of CP800 and DP780 steels and develop a micromechanics-based fracture model to predict edge failure for both reamed and sheared holes. Three-dimensional damage histories were obtained using x-ray microtomography on a series of hole tension specimens interrupted at different strain levels. These experiments considered a tensile specimen with a sheared hole at the center of specimen (sheared edge condition) or reamed (ideal edge condition). Void damage measurements, such as void area fraction, number of voids, void diameter, and void aspect ratio, were conducted and the results are compared to the reamed specimens to isolate the sheared edge effect on damage. The void measurements were used to implement a stress-state dependent model for nucleation, and coupled with the Ragab (2004) model for void growth and the Benzerga and Leblond (2014) model for void coalescence to develop a damage-based material model. Higher damage accumulation was observed behind the sheared edge in comparison the reamed edge at a given strain for both materials considered. An uncoupled anisotropic damage-based fracture model was formulated in a LS-DYNA user-defined material subroutine. As an alternative to computationally expensive multi-stage sheared edge stretching simulations, the measured strain-distribution of the sheared edge was mapped into a finite-element model to predict sheared edge failure. The proposed model was validated for the hole tension testing simulations and found to predict failure accurately for both the CP800 and DP780 for both the edge conditions.

International audience; The objective of this work is to link microstructure features of foamed gypsum (lightweight gypsum board core material) and its compressive properties. Several samples of foamed gypsum with different microstructures were manufactured and characterized by X-ray tomography and 3D image processing. Spherical indentation tests results show that for a similar density, the size distribution of the macropores and the distribution of the three levels of porosity has only a very small influence on the mechanical properties. In contrast, the density and homogeneity of spatial distribution of macropores has a much stronger impact on hardness.

The present study employs in situ X-ray microtomography to characterize the impact of grain size on void nucleation, growth and linkage during tensile loading of magnesium alloy AZ31. It was found that the tensile strain to failure increased almost threefold when the grain size was reduced from 60 to 3 μm. Grain refinement led to reduced twin formation and reduced void growth rates but did not impact markedly on the relationship between strain and the detected void number density. Because the finer grained samples experienced higher strains to failure, greater void number densities were thus detected at failure in these samples. The void volume fraction at failure remained constant despite changing grain size, within error. Final failure occurs via a shear localization and there appears to be a role of void formation in triggering the final shear instability. We thus favour ascribing failure to a void-sheeting type mechanism. Failure is seen to follow rapidly after a critical void volume fraction is attained and this is broadly consistent with predictions made via the application of a simple McClintock model. The higher strains to failure in the present fine-grained samples are thus ascribed chiefly to the lower rates of void growth. The suppression of void growth by grain refinement seen here may explain why finer grain magnesium alloys often display higher tensile ductility.

International audience; Liquid metal dealloying is a promising technique to get nanoporous materials which are attractive for their excellent functional properties. From a (FeCr)x-Ni1−x precursor, it is possible to get porous FeCr with this technique.While immersing precursors in a molten Mg bath, Ni atoms selectively migrate into the Mg bath. After cooling down to room temperature, the resulting microstructure is a bi-continuous structure of FeCr and Mg (with Ni in solid solution). A final etching step removes the Mg solid-state solution phase. Precursors with different compositions were dealloyed and imaged in 3D. From X-ray tomography images, porous FeCr characteristics as solid fraction, phase size, specific surface were extracted. EBSD maps were acquired on samples before and after dealloying.We will show that precursor composition is a key parameter to control pores and grains size while dealloying parameters (time and temperature) are key parameters to control ligaments size and in fine specific surface. By controlling precursor composition and dealloying parameters it is now possible to get dealloyed nanoporous metals with desired grain and porous microstructure by liquid metal dealloying.

International audience; Lightweight plasterboard is a product composed of plaster foam core whose porosity can reach 75 vol%, lined with two sheets of paper. To optimize the trade-o between thermal resistance and mechanical strength, it is important to understand and characterize the mechanical behavior of plasterboard. Core compaction of plasterboard is one of the prevalent degradation mechanism. This mechanism is studied herein using in-situ indentation experiments performed at two dierent scales. The rst test was carried out in a lab tomograph. The second test was conducted on the high resolution synchrotron ID19 beamline at ESRF. Very early damage is revealed. The basic mechanism of pore collapse and its gradual development is detected in contrast with mesoscale observations where compaction appears very abrupt.

International audience; A liquid metal dealloying mechanism is investigated in situ using X-ray tomography and X-ray diffraction. While immersing a FeCrNi precursor alloy in a molten Mg bath, a selective dissolution of Ni atoms into the Mg bath occurs leading to FeCr atom rearrangement. At room temperature, after cooling down, a bicontinuous structure of FeCr and a solid solution of Ni in Mg is obtained. A final etching step is used to remove the Mg solid-state solution phase and form microporous FeCr. 3D dealloying and etching kinetics can be measured using X-ray tomography reconstruction. The evolution of relative strain is analyzed from X-ray diffraction patterns. The different behavior observed during dealloying and etching, depending on the precursor composition is discussed.

The microstructure heterogeneities are compared between inclined and vertical struts of AlSi10Mg lattices processed by Selective Laser Melting. While the vertical struts present a fully dense homogenous microstructure, large levels of porosities and heterogeneous microstructure are present in inclined struts, particularly a much larger level of porosities in the bottom part of the strut compared to the top part. These differences are due to a larger time spent at high temperature for the bottom zone of the strut. A solutionizing and aging heat treatment homogenizes the microstructure but leads to a minor softening due to eutectic spheroidization.

For insulation applications, boards thinner than 2 cm are under design with specific thermal conductivities lower than 15 mW m-1 K-1 . This requires binding slightly hydrophobic aerogels which are highly nanoporous granular materials. To reach this step and ensure insulation board durability at the building scale, it is compulsory to design, characterise and analyse the microstructure at the nanoscale. It is indeed necessary to understand how the solid material is formed from a liquid suspension. This issue is addressed in this paper through wet-STEM experiments carried out in an Environmental Scanning Electron Microscope (ESEM). Latex-surfactant binary blends and latex-surfactant-aerogel ternary systems are studied, with two different surfactants of very different chemical structures. Image analysis is used to distinguish the different components and get quantitative morphological parameters which describe the sample architecture. The evolution of such morphological parameters during water evaporation permits a good understanding of the role of the surfactant.